water level to elevation 1,287.6 feet and create a reservoir in the stream channel about 150 miles long, with a water area of about 120 square miles (77,000 acres). The plan as outlined herein contemplates that, in the wintertime, the reservoir will be drawn down a maximum of 80 feet, thereby making available 5,028,000 acre-feet of storage in years of low run-off for the production of firm power.

Evaporation losses from this reservoir would occur largely in the period from May to September inclusive, when there is always more than enough water to fully meet irrigation and power requirements, hence no allowance has been made for evaporation losses in the operation studies of this reservoir.

Very little information is available upon which to determine the extent of seepage losses from the Columbia River Reservoir. The fact that the reservoir would occupy the river channel, which is largely cut into indurated rocks indicates that seepage losses from the reservoir would be negligible and they have been so assumed in this study.

The tailwater elevation below the proposed power plant at the dam has been assumed to vary with the discharge as at present and ranges from about elevation 933.5 feet with a discharge of 19,000 second-feet to about elevation 981 feet with a discharge of 450,000 second-feet.

Power output.-A study of reservoir operations using monthly estimates of inflow and outflow during the critical periods of low run-off such as occurred in the winters of 1919-20 and 1929-30 shows that with the reservoir drawn down 80 feet there would be sufficient flow to maintain a uniform power output of 920,000 kilowatts, if there were no irrigation and pumping demands for the Columbia Basin project. Further study shows that with the irrigation project fully developed, pumping requirements would reduce the firm power output to 800,000 kilowatts. In this study the overall efficiency of the power plant was taken as 83 per cent and that of the pumping plant as 73 per cent.

A study was made of the joint operations of the Grand Coulee and Columbia River Reservoirs with stream flows as estimated for the period April, 1913, to March, 1931, inclusive. The results of this study are shown graphically on drawing 222-D-5. In this study whenever the Columbia River Reservoir was full, it was assumed that all water, in excess of that pumped to the Grand Coulee Reservoir, to the extent of the power plant capacity (1,575,000 kilowatts) would be passed through the power plant for the production of secondary energy. When the reservoir was not full the releases through the power plant were limited to the water required for the production of firm power and power required for pumping.

The average amounts of the various kinds of power available each year are as follows:

TABLE NO. 4.-Various kinds of power available each year

1 Available only when reservoir is full. Reservoir spills every year so that if a market should arise for such power in the future more could be generated by providing a larger power-plant capacity.

COLUMBIA RIVER DAM

Scope of investigation.-The geological conditions at the site have been studied by Geologist Kirk Bryan and are covered in his_report which is included in the Gault report of 1924. Between July 9, 1921, and January 9, 1922, 14 diamond drill holes were put down at this site by the Columbia Basin Survey Commission. Two additional drill holes were put down in 1930 by the Corps of Engineers, United States Army. The geological report and the record and interpretation of drill holes form the basis for present assumptions as to foundation conditions. The foundation area is so extensive and there is such a deep covering over bedrock that there is much uncertainty as to the actual foundation conditions. A large amount of additional testing is necessary to make a reasonably complete exploration of the foundations. The purpose of additional drilling and testing would be to define the surface of the bedrock more completely over the whole area comprising the foundation of the dam. and power plant, to determine the depth of unsound rock necessary to remove and to determine the presence of major seams or fault zones within the area. To obtain the necessary additional information, the following program of further diamond drilling and testing has been proposed.

Drilling 48 vertical holes, 8,400 linear feet; drilling 10 inclined holes, 8,000 linear feet; trenching 550 linear foot open trench; excavating 4 test pits averaging 150 feet deep.

Estimated cost of additional foundation exploration necessary is $150,000.

southwest of the dam site. Grand Coulee from Coulee City, located approximately 30 miles

routes to the dam site, one connecting with the Great Northern Railrailroad have been made. However, there appears to be two feasible Construction railroad.-No location surveys for a construction

also by a gravel-surfaced county highway going north through miles southeast on the Sunset National Highway (U. S. 10); and improved roads from Mansfield 35 miles west, from Almira about 20 Highways.-The Columbia River dam site can be reached by un

road at Mansfield, 35 miles west, and the other connecting with the Northern Pacific Railroad near Coulee City. A construction cost estimate of a railroad following the latter route was prepared from incomplete United States Geological Survey topography. In addition to providing transportation for the construction of the Columbia River Dam, the Grand Coulee route will also pass near the sites of the proposed north and south Grand Coulee Dams of the proposed Grand Coulee Reservoir. This route will also provide for transportation of concrete aggregates from deposits of this material already accessible by railroad between Coulee City and Hartline, and north of Adrian.

The proposed line, approximately 30 miles in length, will branch from the main line of the Northern Pacific Railroad, near Coulee City Junction, and follow the east side of Grand Coulee at an elevation slightly above the flow line of the proposed Grand Coulee Reservoir to a point opposite the North Grand Coulee Dam, from where the line descends to the west end of the Columbia River Dam.

Transportation of concrete aggregates. For the purpose of estimating the delivered cost of concrete aggregates, it was assumed that the contractor would continue the construction of the railroad down the canyon from the switchback location to a point approximately 2 miles below the dam where the river would be bridged and the railroad constructed upstream to gravel deposits on the east side of the river. It is also practicable to transport concrete aggregates to the mixing plant by an aerial tramway system consisting of several units or lines.

Construction power.-An ample supply of electric power for construction purposes is available from transmission lines of the Washington Water Power Co. which pass through Coulee City. A 60,000volt branch line to Spokane runs parallel to the tracks of the Northern Pacific Railroad, which at a point west of Almira and directly south of the dam site, is but 16 miles distant across the Hartline Plateau.

Concrete materials. With the cooperation of the district engineer, Corps of Engineers, United States Army, Seattle, Wash., preliminary field investigations were made of sand and gravel deposits immediately adjacent to the dam site and of several deposits more remotely situated. Approximately 100 material samples of about 100 pounds each, after removal of cobbles larger than 6 inches, were obtained from the various deposits and shipped to the Bureau of Reclamation laboratory at Denver for test. Brief descriptions of the deposits, the work performed, and the general findings are given in the following paragraphs.

Deposits at dam site.-Extensive bench deposits are located on the east side of Columbia River, adjacent to the dam site. Eight test pits from 21 to 41 feet deep and 10 side-hill trenches from 35 to 66 feet in vertical projection, covering an area about 1 mile north and one-half mile south of the dam center line, were excavated and logs prepared. The average depth of overburden is about 312 feet. The aggregate material lies in horizontal strata, differing widely in gradation, and interspersed with layers of clay at depths of 21 feet or more. Lime-coated and discolored material is found in one test pit. The material is fairly well rounded and generally dirty. It is composed largely of basalt (70 to 80 per cent), with lesser amounts

of granite, shale, quartzite, diorite, and andesite. A small percentage of the basalt is vesicular. The aggregate is apparently sound with the exception of the shale. A total of 89 test samples were taken.

The deposit at the dam site may prove to be a practicable source of aggregate for the dam. Accessibility, apparent soundness and freedom from organic impurities of the material, and the satisfactory size range and gradation of the coarse aggregate are characteristics in its favor. Thorough washing would be essential for removing excess silt, disposing of the softer pieces of shale, and avoiding the formation of clay balls. The extreme variations in gradation of the sand, even in the same pit, point to the possible need for division of the same into two or three sizes and recombination in desired proportions. Without such separation, the high average fineness modulus of the washed sand would require correction, by one of a number of possible means. While the tabular values for average pit run proportions show a large excess of sand, it is probable that the actual average percentage of sand is materially less, due to the fact that thick layers of coarse material, especially in the trenches, were not sampled and had to be disregarded in arriving at the figures stated. Additional investigations would be required to obtain more reliable data and to definitely establish the sufficiency of the deposits. Mansfield pit.-This pit is located in sec. 35, T. 30 N., R. 29 E., about 10 miles in direct line northwest of the Columbia River dam site. It is apparently a small deposit containing relatively fine material only. The material is similar in composition and shape of particles to that at the dam site. Only one sample was taken.

The Mansfield deposit, considered alone, is apparently of little value for the purpose, owing to its limited extent, the large proportion and high fineness modulus of the sand, and a pronounced deficiency in the larger sizes of gravel.

Adrian pit. This is an extensive deposit located along the Northern Pacific Railroad about 1 mile north of Adrian and 42 miles in direct line southwest of the dam site. The face of the deposit is about 600 feet long and 75 feet high, with the lower half covered by talus. The material is apparently clean, structurally sound, and fairly well rounded. It is composed entirely of basalt with vesicles present in 15 to 25 per cent of the coarse aggregate. Four samples were taken from the upper half of the face.

The Adrian deposit is handicapped by its distance from the dam site, its excess of sand, and the relatively high fineness modulus of the sand. The deposit is apparently clean and extensive and, with the exception of the deposits at the dam site, shows the most favorable gradation of coarse aggregate.

Hartline pit. This is an extensive deposit located along the Northern Pacific Railroad and the power line of the Washington Water Power Co. about 21 miles in direct line southwest of the dam site. It lies about 6 miles east of Coulee City and 3 miles west of Hartline. The exposed face of the deposit is about 500 feet long and 30 feet high and the pit is covered with an earth overburden about 4 feet deep. The material is apparently clean, structurally sound and fairly well rounded. It is composed entirely of basalt with vesicles prominent in 30 to 50 per cent of the coarse aggregate. The face